Dynamics of a Nitrogen Leidenfrost Droplet on a Water pool*

The Leidenfrost effect for a nitrogen droplet on a water pool at its freezing temperature is studied experimentally and theoretically, with attention on the processes taking place both on top and below of the water meniscus. The temporal evolution of the droplet size and the ice formation inside the pool are captured in a top-view and a side-view using a high-speed video system. The amount of ice present in the pool after thermal relaxation is used to measure the total heat actually transferred between the droplet and the pool.

The theoretical model presented by Maquet et al. [L. Maquet et al., Phys. Rev. Fluids 1(5), 053902, (2016)] for the shape of the droplet and the pool surface in that situation is used as the basis for transient modeling of the droplet shrinkage. It is extended to also account for heat transfer from the gaseous ambient, and assuming quasi-steady droplet evaporation the model is numerically solved in order to predict the temporal evolution of the droplet diameter. A comparison of the model predictions for droplet shrinkage with the experimental data reveals perfect agreement. Finally, also the predictions for the total heat transfer between the droplet and the pool well agree with the heat corresponding to the experimentally measured ice in the pool.